Optical sources are included in a variety of optical measurement and communication systems. However, many types of optical sources experience wavelength drift, induced by changes in temperature, pressure or other operating conditions, that impairs the performance of the systems in which the optical sources are included. Wavelength drift also causes undesired variations in power-weighted wavelength of the optical source, especially when the optical source provides optical signals that are widely spaced relative to the gain profile of the optical source.
Known techniques apply either a feedback signal or a correction signal to a wavelength modulation port of an optical source in order to reduce wavelength drift. In one technique, a feedback signal applied to the wavelength modulation port cancels wavelength drift and maintains a constant power-weighted wavelength at the output of the optical source. Generating the feedback signal relies on optical detectors and feedback circuitry, which increases the manufacturing cost of the optical source. Another technique reduces wavelength drift by applying a correction signal to the wavelength modulation port of the optical source to approximately cancel wavelength drift and reduce the variations in power-weighted wavelength of the optical source. Establishing the correction signal involves characterizing the wavelength drift of the optical source according to temperature, pressure and other operating conditions of the optical source, which is time-consuming.
A method and apparatus constructed according to the preferred embodiments of the present invention accommodate for wavelength drift of an optical source without the disadvantages associated with applying either a feedback signal or a pre-established correction signal to the optical source. The apparatus includes an optical source having a wavelength control port and an output port providing one or more optical signals. The one or more optical signals has a wavelength that drifts at a first rate. A signal generator within the apparatus provides a control signal to the wavelength control port of the optical source that causes wavelength variations to be superimposed on the wavelength drift of the one or more optical signals. The superimposed wavelength variations occur at a second rate that exceeds the first rate. The apparatus also includes a receiver coupled to the output port of the optical source, that receives the one or more optical signals having the superimposed wavelength variations. The receiver accommodates for the wavelength variations caused by the control signal, enabling a received wavelength to be distinguished from the drifting wavelength of the optical source.
According to a first preferred embodiment of the present invention, the superimposed wavelength variations within the apparatus are distributed over a wavelength range so that the wavelength variations caused by the control signal have a predefined average wavelength. According to a second preferred embodiment of the present invention, the superimposed wavelength variations within the apparatus follow a predefined contour. The preferred embodiments of the present invention are alternatively implemented in a corresponding method for accommodating for wavelength drift of optical sources.